Are you talking the the lower reverse gear, the reverse idler, or the 1st/Reverse slider? In my opinion, changing any one would require changing of all three of these plus the lower first gear due to them wearing all together.

You have to split the tractor at the transmission to slide the main shaft forward to allow you to change the slider gear. This opens a can of worms in terms of "while you are there, you may as well ..........."